Density = mass/volume
Volume = mass/density
This is a problem I have at work with quantifying earth removal. Different soils have different bulk densities. Topsoil may have a density of 1.4Mg/m³, clay may be 2.1Mg/m³, but they both vary based on composition. Movement of material is all priced on volume, with accurate densities being unknown, then material gets moved by weight... Urgh! Anyway, honey is the same in that sugar and water content varies (although not as much as earth).
In an equally confusing fashion, the 8oz jar I just filled with water only comfortably held 165ml. I was expecting it to hold 227ml (8oz being 227g), but it doesn't. Divide 227 by 1.33 and you get 162, not far off. Coincidentally, 1.33 is close to the factors you mentioned. Maybe 1.33 is the density of jam, I don't know.
I also saw one website that specifies jars as '370ml (1lb)' and '228ml (8oz)'. There's something wrong there if 1lb = 453g and 8oz = 227g. Traditionally, jar sizes are based on weight so it's probably best to ignore the volumes and buy jars based on advertised weights. If only volume is given, I'd assume this is volume of jam with a density of 1.33 and not water.
I buy jars advertised as holding a certain weight, I place one on the scale, tare (zero) the scale then add honey until I achieve the required weight (either 227g or 340g in my case).